Towards the Highly Efficient Synthesis and Selective Methylation of C(sp³)‐Bridged [6]Cycloparaphenylenes from Fluoren[3]arenes

Abstract

An approach to the highly efficient synthesis of C(sp3)-bridged [6]cycloparaphenylenes (C[6]CPPs)f rom fluoren[3]arenes (F[3]As)w as developed. Consequently, F[3]As as anew kind of macrocyclic arenes were synthesized. Followed by the demethylation, triflation and intramolecular aryl-aryl coupling reactions, C[6]CPPs were then conveniently obtained. Interestingly, C[6]CPPs could be selectively methylated to produce their fully outer-methyl-substituted derivatives.T he crystal structures showed the hydroxyl-substituted F[3]As had bowl-shaped conformations,a nd the C[6]CPPs exhibited rigid belt-shaped structures with deep cavities.Moreover, C[6]CPPs exhibited high HOMO energies and narrowe nergy gaps.A nu nclosed belt was further obtained, and it not only showed as imilar narrowe nergy gap to those of the aromatic belts,b ut also displayed strong fluorescence property,whichcan play avital role in the design and synthesis of new aromatic belts.

Towards the Highly Efficient Synthesis and Selective Methylation of C(sp3)‐Bridged [6]Cycloparaphenylenes from Fluoren[3]arenes

“…Themain interactions in the packing mode of C[6]CPP5 were .Hydrogen atoms are omitted for clarity. [39] Angewandte Chemie Forschungsartikel found to be the intermolecular C(sp 3 )-H•••p interactions between the adjacent molecules of C [6]CPP5 with the distances of 2.829 and 2.880 ,a nd the intermolecular C(sp 2 )-H•••p interaction with an average distance of 2.834 (Figure S90).…”

“…However,itwas surprisingly found that if am ixture solvents of C 6 D 6 and Hydrogen atoms not involved in the non-covalent interactions were omitted for clarity. [39] Tabelle 1: The Optimization of aryl-aryl coupling reaction from 2,7-OTf- S51), in which one singlet at 7.73 ppm belonged to the aromatic proton, while the inner and outer protons of the methylene groups showed two doublets at 4.15 and 3.83 ppm, respectively.T his result also indicated its high D 3d symmetric structure.Moreover,the red crystal of C [6]CPP1 could be obtained by slow diffusion of methanol into aC H 2 Cl 2 solution of C [6]CPP1 at room temperature.T he crystal structure showed C [6]CPP1 had ac ylindrical shape-like structure with an average diameter and cavity depth 7.766 and 3.971 ,r espectively,a nd an average CÀCsingle bond that connected the phenylene units was 1.475 ,w hich were all consistent with those of the Itamisreport. [22] Since C[6]CPP2 showed good solubility in benzene,i ts 1 HNMR spectrum in C 6 D 6 was then performed.…”

“…As shown in Figure 4c, UB exhibited ac omparatively complex 1 HNMR spectrum in CD 2 Cl 2 .A ccording to the 2D NOESY spectrum (Figure 4d), the NOE signals between aromatic protons and the inner protons of the methylene and methyl groups enabled us to give af ull assignment of the six singlets for the aromatic protons.With the aid of 1 H- 13 CHSQC spectrum (Figure 4e), H7/H8 and H9/H10 could be easily distinguished to the outer and inner protons of the two methylene groups, respectively.Moreover,two singlets H13 and H14 at 1.82 ppm and 1.18 ppm were assigned to the methyl protons of one C(CH 3 ) 2 ,w hile two singlets H11 and H12 at 1.38 ppm and 1.14 ppm was assigned to the methyl protons of another C(CH 3 ) 2 .I nterestingly,i tw as further found that UB showed and e) partial 1 H- 13 CHSQC spectrum of C [6]CPP2 in C 6 D 6 . [39] 13 CHSQC spectrum of UB. [39] Angewandte Chemie Forschungsartikel 13134 www.angewandte.de strong fluorescence under 365 nm UV lamp probably due to the two strong electron-deficient triflate groups,w hich was obviously different from those of the aromatic belts C- [6]CPPs with fully carbon conjugated structures.M olecule UB could not only be very helpful for us to understand the formation process of the aromatic belt, but also be of great meaningfulness to further design new systems with specific structure and property.…”

“…[39] 13 CHSQC spectrum of UB. [39] Angewandte Chemie Forschungsartikel 13134 www.angewandte.de strong fluorescence under 365 nm UV lamp probably due to the two strong electron-deficient triflate groups,w hich was obviously different from those of the aromatic belts C- [6]CPPs with fully carbon conjugated structures.M olecule UB could not only be very helpful for us to understand the formation process of the aromatic belt, but also be of great meaningfulness to further design new systems with specific structure and property.…”

“…Figure 5. a) Chemical structure and the 1 HNMR spectrum (500 MHz, C 6 D 6 :CD 2 Cl 2 = 4:1, 298 K) of C[6]CPP4.b )Chemical structure and the 1 HNMR spectrum (500 MHz, C 6 D 6 ,298 K) of C[6]CPP5.c)T op view and side view of crystal structure of C[6]CPP4.d )T op view and side view of crystal structure of C[6]CPP5.Hydrogen atoms are omitted for clarity [39]. …”